1. Field of the Invention
The present invention relates to novel methods of detecting and measuring levels of the tumor growth factor pleiotrophin (PTN). These measurements can be used to determine the presence of PTN-positive diseases, to determine the relative prognosis of the disease, to determine the efficacy of cytotoxic anticancer drugs, and for molecular targeting of PTN. More particularly, the present invention relates to immunoassays using anti-PTN antibodies to detect and measure levels of PTN in samples. The present invention also relates to kits for detecting and measuring PTN levels.
2. Description of the Related Art
Tumor expansion and metastasis are dependent on growth factors produced by the tumor cells and/or by the stroma (Folkman J, N. Engl. J. Med. 333: 1757–1763, 1995) and one would expect in particular that these growth factors, such as angiogenic factors that target sprouting blood vessels, can be shed into the circulation and hence may provide a direct measure of tumor progression. With respect to the significance of growth factor expression and release into the circulation, several clinical studies found elevated levels of basic fibroblast growth factor (bFGF) in the sera of patients with cancer of the prostate (Meyer et al., Cancer, 76: 2304–2311, 1995), breast (Sliutz et al., Anticancer Res., 15: 2675–2677, 1995), cervix uteri (Sliutz et al., Cancer Lett., 94: 227–231, 1995) and kidneys (Duensing et al., Anticancer Res., 15: 2331–2333, 1995) as well as in the urine of patients with a wide spectrum of different cancers (Nguygen et al., J. Natl. Cancer Inst., 86: 356–360, 1994). These clinical findings and studies in animals (Soutter et al., Cancer Research, 53: 5297–5299, 1993) suggest that in principle angiogenic factors released from tumors can enter the circulation and may serve as useful indicators of tumor progression or as surrogate endpoints of therapeutic efficacy (Wellstein et al., J. Natl. Cancer Inst., 86:328–329).
The tumor growth factor pleiotrophin (PTN) belongs to a family of growth factors that includes midkine (MK) (Kadomatsu et al., Biochem. Biophys. Res. Commun., 3: 1312–1318, 1988). PTN and MK share 50% sequence homology (Laaroubi et al., Prog. Growth Factor Res., 6(1): 25–34, 1995). PTN is involved in growth and differentiation processes that are tightly regulated during development (Schulte et al., Tumor Angiogenesis, pp. 273–289, Oxford University Press, 1997), and it is a mitogen for fibroblasts (Fang et al., J. Biol. Chem., 267: 25889–25897, 1992), epithelial cells and endothelial cells (Fang et al., J. Biol. Chem., 267: 25889–25897, 1992 and Delbe et al., J. Cell Physiol., 164: 47–54, 1995). PTN also stimulates plasminogen activator production (Kojima et al., Biochem. Biophys. Res. Commun., 216: 574–581, 1995), induces tube formation of endothelial cells in vitro (Laaroubi et al., Prog. Growth Factor Res., 6(1): 25–34, 1995), and thus can serve as a tumor angiogenesis factor in vivo. Further, PTN is expressed in a variety of tumor cell lines and tumor samples (Fang et al., J. Biol. Chem., 267: 25889–25897, 1992), and pleiotrophin has been found to be oncogenic when over-expressed in NIH3T3 cells (Chauhan et al., Proc. Natl. Acad. Sci., 90: 679–682, 1993) and SW-13 human adrenal carcinoma cells (Fang et al., J. Biol. Chem., 267: 25889–25897, 1992). Furthermore, the growth, angiogenesis and metastasis of PTN-positive melanomas (Czubayko et al., Biol. Chem., 269: 21358–21363, 1994 and Czubayko et al., Proc. Natl. Acad. Sci., 93: 14753–14758, 1996) and the invasion and angiogenesis of choriocarcinoma (Schulte et al., Proc. Natl. Acad. Sci., 93:14759–14764, 1996) was reverted by depleting the tumor cells of their endogenous PTN with specific ribozymes.
Knowing the levels of PTN in samples can play a significant role in diagnosing and prognosticating PTN-positive diseases, monitoring the efficacy of anti-PTN therapeutics, and detecting PTN inhibitors or stimulators. Accordingly, there is a need in the art for methods to detect and measure levels of pleiotrophin in samples and to diagnose pleiotrophin-positive diseases. There is also a need in the art for methods to monitor the effectiveness of therapeutic treatments for pleiotrophin-positive diseases and to test for agents or drugs that inhibit or stimulate pleiotrophin.